The needs for travel and consumer goods have driven the ever increasing consumption of fossil fuels such as coal and oil, typically obtained from deep underground. The extraction of fossil fuels by mining and drilling has often been accompanied by environmental and political costs. Furthermore, as the more accessible sources of fossil fuels are being used up, this has led to the pursuit of more expensive extraction technologies such as fracking and deep sea drilling. Additionally, the consumption of fossil fuels causes higher levels of atmospheric carbon, typically in the form of carbon dioxide.
To reduce these problems, there have been extensive efforts made in converting biomass to fuels and other useful chemicals. Unlike fossil fuels, biomass is renewable and carbon-neutral; that is, biomass-derived fuels and chemicals do not lead to increased atmospheric carbon since the growth of biomass consumes atmospheric carbon.
Much of the work on biomass has involved converting refined biomass including vegetable oils, starches, and sugars; however, since these types of refined biomass may alternatively be consumed as food, there is even a greater utility for converting non-food biomass such as agricultural waste (bagasse, straw, corn stover, corn husks, etc.), energy crops (like switch grass and saw grass), trees and forestry waste, such as wood chips and saw dust, waste from paper mills, plastic waste, recycled plastics or algae, in combination sometimes referred to as cellulosic biomass. Biomass generally includes three main components: lignin, hemicellulose, and cellulose.
Generating fuels and chemicals from biomass requires specialized conversion processes different from conventional petroleum-based conversion processes due to the nature of the feedstock. High temperatures, solid feed, high concentrations of water, unusual separations, and oxygenated by-products are some of the features of biomass conversion that are distinct from those encountered in petroleum upgrading. Thus, despite extensive efforts, there are many challenges that must be overcome to efficiently produce chemicals or fuels from biomass. Such challenges include the tendency of the heavy hydrocarbons, aromatics, and oxygenates manufactured by catalytic fast pyrolysis to form a sticky tar-like substance that easily deposits on tubes and downstream equipment if not reduced or eliminated from the process streams.
A variety of biomass-derived polymeric materials such as lignin, cellulose, and hemicellulose, can be pyrolyzed to produce mixtures of aromatics, olefins, carbon monoxide (CO), carbon dioxide (CO2), water, and other products. A particularly desirable form of pyrolysis is known as catalytic fast pyrolysis (CFP) which involves the conversion of biomass in a catalytic fluid bed reactor to produce a mixture of aromatics, olefins, and a variety of other materials. The aromatics include benzene, toluene, xylenes (collectively BTX), and naphthalene, among other aromatics. The olefins include ethylene, propylene, and lesser amounts of higher molecular weight olefins.
The raw effluent from a CFP process is a complex mixture that comprises aromatics, olefins, oxygenates, paraffins, H2, CH4, CO, CO2, water, char, ash, coke, catalyst fines, and a host of other compounds. Manufacture, separation, and recovery of the various components, especially those found to be more valuable, from this complex mixture is increasingly important.
In U.S. Patent Publication No. 2014/0107306 A1, a method and apparatus are described for pyrolysis of biomass and conversion of at least one pyrolysis product to another chemical compound. The latter method comprises feeding a hydrocarbonaceous material to a reactor, pyrolyzing within the reactor at least a portion of the hydrocarbonaceous material under reaction conditions sufficient to produce one or more pyrolysis products, catalytically reacting at least a portion of the pyrolysis products, separating at least a portion of the hydrocarbon products, and reacting a portion of the hydrocarbon products to produce a chemical intermediate.
In U.S. Pat. Nos. 8,277,643 and 8,864,984; U. S. Patent Publication Nos. 2012/0203042 A1, 2013/0060070 A1, 2014/0027265 A1, and 2014/0303414 A1, each incorporated herein by reference in its entirety, apparatus and process conditions suitable for CFP are described.
It is a general goal of this technology to provide high yields of useful products, such as BTX, usually the most valuable products, with reduced or eliminated production of tar-like substances. Under operating conditions currently employed in CFP, heavy hydrocarbons having a tendency to form sticky, tar-like substances (“fouling” or “gunk”) are manufactured. This fouling/gunk easily deposits on tubes and downstream equipment.
In U.S. Pat. No. 7,905,990, it appears that fouling may be mitigated in a non-catalytic thermal biomass conversion process by directing the hot vapor stream from the reactor to at least one condensing chamber where the hot vapor stream is rapidly cooled by flow of a quench media. In U. S. Patent Publication No. 2012/0167452 A1, a non-catalytic thermal biomass conversion process is described where a solvent selected from the group consisting of hydrocarbon solvent, substituted hydrocarbon solvent, and combinations thereof, is used as a quench fluid. The hot biomass pyrolysis products are contacted with quench fluid in absorption and quench apparatus.
In U. S. Patent Application No. 2016/0040077, a process and system for hydroprocessing biopyrolysis oils is provided that includes the rejuvenation of a partially flow constricted reactor by flushing with a flushing agent at reduced temperatures. The process requires the reactor system to be cooled to facilitate the rejuvenation, and hence must be conducted in an intermittent fashion and cannot be conducted in a continuous fashion.
In U. S. Patent Application 2014/0102874, a pyrolysis process is provided to remove coke and tar as a flushing fluid is applied or injected directly into a regenerative pyrolysis reactor operated in a cyclic or periodic manner No provision is made for continuous production as the reactor is operated in a sequence of alternating heating and regeneration steps.
In light of current commercial practices and the disclosures of art, a simple economical process for enhancing production of useful products with reduced or eliminated fouling from a catalytic fast pyrolysis process is needed. The present invention provides such a process.